Calibration Method of LiDAR and LiDAR

Abstract

The present invention provides a calibration method for a lidar, comprising: emitting a detection pulse towards a target; receiving an echo pulse after the target reflects the detection pulse; obtaining distance information of the target according to the detection pulse and the echo pulse; obtaining a calibration reference quantity of the echo pulse, the calibration reference quantity being based on the intensity change of the echo pulse; calibrating the obtained distance information according to the calibration reference quantity. Using this calibration method to calibrate the flight time of the lidar can improve the ranging performance of the lidar, and the calibration accuracy is also significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of laser detection, and in particular to a laser radar calibration method and a laser radar using the calibration method. Background Art

[0002] LiDAR (LiDAR) is a device that uses optical methods to accurately measure distances. It has applications in obstacle detection, geological modeling, position acquisition, robotics, and unmanned vehicles. The distance to a target is calculated by measuring the time it takes for a transmitted light beam to travel from the target to the LiDAR. Scanning across different locations in three-dimensional space generates point cloud data, enabling the user to perceive the surrounding environment. Time-of-flight (TOF) calibration is crucial for accurate LiDAR ranging. Together with hardware design, it determines key LiDAR metrics such as range performance and accuracy. LiDAR calibration primarily involves the selection of calibration reference quantities and the design of calibration methods. The former requires selecting a monotonic and stable reference quantity within the LiDAR's range, while the latter requires designing a method that optimizes the performance of the selected signal. Therefore, the TOF calibration method directly determines the LiDAR's ranging performance.

[0003] Common calibration methods in the prior art include: pulse width calibration, which uses the pulse width information of the echo signal within the measurement range to correct the ranging deviation caused by the change in echo energy; in addition, the echo energy is measured by integration, and the current integral of the echo signal within the measurement range is used to perform flight time calibration to correct the ranging deviation.

[0004] The contents of the background technology section are merely technologies known to the public and do not necessarily represent the existing technologies in this field. Summary of the Invention

[0005] The calibration method in the prior art has a large error. In order to improve the accuracy of calibration, the present invention provides a calibration method for a laser radar, comprising:

[0006] Sending a detection pulse to the target;

[0007] Receive the echo pulse after the detection pulse is reflected by the target object;

[0008] Acquiring distance information of the target object according to the detection pulse and the echo pulse;

[0009] Acquiring a calibration reference quantity of the echo pulse, wherein the calibration reference quantity is based on an intensity change of the echo pulse;

[0010] The obtained distance information is calibrated according to the calibration reference amount.

[0011] According to one aspect of the present invention, the distance information is calculated based on the time of flight determined from the detection pulse and the echo pulse; wherein the time of flight is determined based on the pulse front times of the detection pulse and the echo pulse.

[0012] According to one aspect of the present invention, the calibration reference quantity is used to calibrate the time of flight.

[0013] According to one aspect of the present invention, the calibration reference quantity varies monotonically according to the change in the intensity of the echo pulse.

[0014] According to one aspect of the present invention, obtaining the calibration reference quantity of the echo pulse includes:

[0015] Obtaining the front slope value of the echo pulse; and / or

[0016] Obtaining the intensity peak value of the echo pulse.

[0017] According to one aspect of the present invention, the steps of obtaining the calibration reference quantity of the echo pulse include:

[0018] According to the first threshold VL, obtaining the first moment T1 corresponding to the front edge of the echo pulse and the second moment T2 corresponding to the trailing edge of the echo pulse;

[0019] According to the second threshold VH, obtaining the third moment T3 corresponding to the front edge of the echo pulse and the fourth moment T4 corresponding to the trailing edge.

[0020] According to one aspect of the present invention, the steps of obtaining the front slope value of the echo pulse include:

[0021] Based on the intensity difference between the second threshold VH and the first threshold VL, and the time difference between the third moment T3 and the first moment T1, obtaining the front slope value SL of the echo pulse.

[0022] According to one aspect of the present invention, the steps of obtaining the intensity peak value of the echo pulse include:

[0023] Obtaining the low threshold pulse width WL based on the time difference between the first moment T1 and the fourth moment T4, and obtaining the high threshold pulse width WH based on the time difference between the second moment T2 and the third moment T3;

[0024] Based on the low threshold pulse width WL, the high threshold pulse width WH, the first threshold VL, and the second threshold VH, obtaining the intensity peak value PV of the echo pulse.

[0025] According to one aspect of the present invention, the step of obtaining a first moment T1 corresponding to the leading edge of the echo pulse and a second moment T2 corresponding to the trailing edge of the echo pulse according to the first threshold VL, and obtaining a third moment T3 corresponding to the leading edge of the echo pulse and a fourth moment T4 corresponding to the trailing edge according to the second threshold VH includes:

[0026] Input the echo pulse signal to the non-inverting terminal of the first comparator, input the first threshold VL to the inverting terminal of the first comparator. When the comparison result between the intensity of the echo pulse and the first threshold VL flips for the first time, obtain the first moment T1 through a time-to-digital converter. When the comparison result between the intensity of the echo pulse and the first threshold VL flips for the second time, obtain the second moment T2 through a time-to-digital converter;

[0027] Input the echo pulse signal to the non-inverting terminal of the second comparator, input the second threshold VH to the inverting terminal of the second comparator. When the comparison result between the intensity of the echo pulse and the second threshold VH flips for the first time, obtain the third moment T3 through a time-to-digital converter. When the comparison result between the intensity of the echo pulse and the second threshold VH flips for the second time, obtain the fourth moment T4 through a time-to-digital converter.

[0028] According to one aspect of the present invention, the step of calibrating the obtained distance information according to the calibration reference quantity includes:

[0029] Calibrate the distance information through a calibration curve according to the calibration reference quantity.

[0030] According to one aspect of the present invention, the echo pulse is detected by a silicon photomultiplier or a single-photon avalanche diode array and an electrical signal is output.

[0031] According to one aspect of the present invention, the calibration method further includes:

[0032] Select different calibration reference quantities according to different measurement range to calibrate the distance information.

[0033] The present invention also provides a lidar configured to use the calibration method as described above to calibrate the distance information.

[0034] A preferred embodiment of the present invention provides a calibration method for a lidar and a method for obtaining an appropriate calibration reference quantity. The calibration reference quantity monotonically changes with the intensity of the echo pulse within the measurement range. Using it to calibrate the flight time of the lidar can improve the ranging performance of the lidar, and the calibration accuracy is also significantly improved. Description of the Drawings

[0035] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the accompanying drawings:

[0036] Figure 1 Schematically shows the echo signal of an existing lidar including a light receiving device and an analog-to-digital converter;

[0037] Figure 2 Schematically shows the internal structure of the light receiving device of the present invention;

[0038] Figure 3 Schematically shows the echo signal of the lidar of the present invention including a light receiving device and a time-to-digital converter;

[0039] Figure 4 Shows the calibration method of the lidar according to a preferred embodiment of the present invention;

[0040] Figure 5 Schematically shows a method for obtaining the time of flight of the lidar of the present invention;

[0041] Figure 6 Schematically shows the time extraction error under different echo intensities of the present invention;

[0042] Figure 7A Shows the method for obtaining the slope value of the echo pulse front edge according to a preferred embodiment of the present invention;

[0043] Figure 7B Schematically shows the principle of obtaining the slope value of the echo pulse front edge according to a preferred embodiment of the present invention;

[0044] Figure 8A Shows the method for obtaining the peak value of the echo pulse intensity according to a preferred embodiment of the present invention;

[0045] Figure 8B Schematically shows the principle of obtaining the peak value of the echo pulse intensity according to a preferred embodiment of the present invention;

[0046] Figure 9A and 9B Schematically shows the specific implementation structure for obtaining the parameters in the echo pulse according to a preferred embodiment of the present invention;

[0047] Figure 10 Shows the method for obtaining the calibration curve according to a preferred embodiment of the present invention;

[0048] Figure 11 Schematically shows the lidar according to a preferred embodiment of the present invention. Detailed implementation manners

[0049] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than restrictive.

[0050] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0051] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection: it can be a mechanical connection, an electrical connection or can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] In the present invention, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature may include the direct contact between the first and second features, or may include the situation where the first and second features are not in direct contact but are in contact through other features between them. Moreover, the first feature being "above", "over" and "on top of" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature includes that the first feature is directly below and obliquely below the second feature, or merely indicates that the horizontal height of the first feature is lower than that of the second feature.

[0053] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numerals and / or reference letters in different examples. This repetition is for the purpose of simplification and clarity and does not itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0054] Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the embodiments described herein are only for the purpose of illustrating and explaining the present invention and are not intended to limit the present invention.

[0055] For a lidar based on time-of-flight ranging, its light emitting device emits laser emission pulses with a narrow pulse width. The laser emission pulses are incident on an object and reflected by the object to form laser echo pulses. The lidar obtains the distance information of the objects around it by using the time difference between the obtained laser echo pulses and the laser emission pulses, using d = c * t / 2, where c is the speed of light and t is the time of flight.

[0056] As Figure 1 shown, the echo signal received by the light receiving device of the existing lidar, where the echo signal is an echo pulse signal, and the pulse width of the echo signal shows a monotonic characteristic with the change of the echo intensity. Specifically, by collecting data of the echo signal from strong to weak and performing piecewise linear fitting, a more accurate calibration result can be obtained.

[0057] However, in a lidar that uses a silicon photomultiplier (SiPM) as the light receiving device and a time-to-digital converter (TDC) to sample the output signal, there is no monotonic correspondence between the pulse width of the echo signal and the ranging error. Therefore, the pulse width cannot be used for calibration. The internal structure of the silicon photomultiplier 11 is as Figure 2As shown in the figure, the most basic unit of the silicon photomultiplier tube 11 is a pixel unit (Pixel) (shown by the dashed box in the figure) composed of a single photon avalanche diode (SPAD) 111 operating in Geiger mode and a quenching resistor 112 connected in series. Multiple pixel units are arranged in a two-dimensional direction to form the silicon photomultiplier tube 11. The working process of the silicon photomultiplier tube 11 is as follows: when a single photon enters a pixel unit, if the photon is detected by the pixel unit, it will cause an avalanche in the single photon avalanche diode 111 in the pixel unit. The charge accumulated in the junction capacitance ( Figure 1 not shown) of the single photon avalanche diode 111 flows from the anode to the cathode, the bias voltage across the single photon avalanche diode 111 drops, the avalanche stops, and the voltage change amount ΔV across the single photon avalanche diode 111 is output through the fast output capacitor 113. Then, the quenching resistor 112 charges the junction capacitance of the single photon avalanche diode 112 to restore it to Geiger mode. Only when the single photon avalanche diode 111 is restored to Geiger mode can it continue to respond to the next photon. The time for the quenching resistor 112 to charge the junction capacitance of the single photon avalanche diode 111 is the recovery time of the single photon avalanche diode 111.

[0058] When multiple photons enter different pixel units, multiple single photon avalanche diodes 111 will be triggered to cause avalanches. In this way, multiple fast output capacitors 113 connected to the multiple avalanche photodiodes 111 will output the voltage change amounts of each single photon avalanche diode 111. The voltage change amounts output by the multiple single photon avalanche diodes 111 are accumulated and the total voltage change amount ΔV is output. The more the number of single photon avalanche diodes 111 that have avalanches, the greater the accumulated total voltage change amount ΔV output; the more the number of single photon avalanche diodes 111 that have avalanches, the more the charge quantity for charging the junction capacitance in the single photon avalanche diode 111 through the quenching resistor, that is, the greater the generated charging current.

[0059] As Figure 3 shown, since the silicon photomultiplier tube is composed of multiple pixel units, when a strong signal light is incident, multiple single photon avalanche diodes are triggered simultaneously, and the output signal is the superposition of the response waveforms of each single photon avalanche diode, and the leading edge of the echo signal is steep; while the time of the trailing edge of the echo signal is determined by the circuit characteristics of the silicon photomultiplier tube itself. The recovery time of the silicon photomultiplier tube is determined by the charging time constant of the RC circuit. Since the quenching resistor inside the silicon photomultiplier tube is relatively large, the time of the trailing edge of the echo signal will be relatively long.

[0060] From Figure 3It can be seen that as the echo signal strengthens, the leading-edge slope of the response waveform (output voltage or output current) of the silicon photomultiplier tube shows a monotonically increasing trend, and the intensity peak of the echo signal also shows a monotonically increasing trend.

[0061] According to a preferred embodiment of the present invention, as Figure 4 shown, the present invention provides a calibration method 10 for lidar, including:

[0062] In step S101, a detection pulse is emitted towards the target to measure the distance of the target relative to the lidar.

[0063] In step S102, the echo pulse after the target reflects the detection pulse is received, that is, the echo pulse corresponding to the transmitted pulse is received.

[0064] In step S103, the distance information of the target is obtained based on the detection pulse and the echo pulse.

[0065] According to a preferred embodiment of the present invention, the distance of the target relative to the lidar is calculated based on the flight time determined by the transmitted pulse and the echo pulse, where the flight time is determined based on the pulse leading-edge times of the transmitted pulse and the echo pulse. As Figure 5 shown, the rising edge moment of the transmitted pulse is extracted according to the transmitted signal threshold as the transmission moment; the rising edge moment of the echo pulse is extracted according to the echo signal threshold as the reception moment. Then the flight time is obtained according to the time difference between the transmission moment and the reception moment.

[0066] In step S104, a calibration reference quantity of the echo pulse is obtained, and the calibration reference quantity varies based on the intensity of the echo pulse.

[0067] According to a preferred embodiment of the present invention, the calibration reference quantity is used to calibrate the flight time, and then the distance between the target and the lidar is calculated based on the flight time. The principle is as follows: As Figure 6 shown, for the echo pulses reflected by different targets (such as the reflected echo 1 and reflected echo 2 in the figure), the reception moments are extracted, and there will be a certain deviation in the extracted reception moments. Due to different echo intensities, the deviation of time information extraction is caused, and further the error in flight time calculation is caused. Since the measurement error caused by different echo intensities is large, it is necessary to calibrate the measured flight time. The prerequisite for flight time calibration is to be able to find a reference quantity related to the measurement error, and the reference quantity should have a monotonic correspondence relationship with the measurement error, otherwise it cannot be calibrated.

[0068] According to a preferred embodiment of the present invention, in order to improve the accuracy of calibration, a reference quantity that monotonically changes according to the change in the intensity of the echo pulse can be selected for calibration. In the preferred embodiment of the present invention, a reference quantity that is monotonic and has good stability within the measurement range is selected to calibrate the flight time. These calibration reference quantities include:

[0069] The leading edge slope value of the echo pulse; and / or

[0070] The intensity peak value of the echo pulse.

[0071] In step S105, according to the calibration reference quantity, the acquired distance information is calibrated.

[0072] It can be known from Figure 3 that the leading edge slope value and the intensity peak value of the echo pulse are both reference quantities that monotonically change within the measurement range with the change in the intensity of the echo pulse. Using the leading edge slope value and / or the intensity peak value of the echo pulse to calibrate the flight time of the lidar, for example, calibrating the reception time of the echo pulse according to the leading edge slope value and / or the intensity peak value of the echo pulse, so as to realize the calibration of the flight time, and further more accurate distance information can be obtained.

[0073] According to a preferred embodiment of the present invention, as Figure 7A , Figure 7B shown, the present invention provides a method 20 for obtaining the leading edge slope SL of the echo pulse, including:

[0074] In step S201, a first threshold value VL and a second threshold value VH are set;

[0075] In step S202, according to the first threshold value VL, the first moment T1 corresponding to the leading edge of the echo pulse is obtained;

[0076] In step S203, according to the second threshold value VH, the third moment T3 corresponding to the leading edge of the echo pulse is obtained;

[0077] In step S204, according to the signal intensity difference between the second threshold value VH and the first threshold value VL, and the time difference between the third moment T3 and the first moment T1, the leading edge slope value SL of the echo pulse is obtained. Specifically, as Figure 7B shown, calculate the slope of the triangular area shown in the figure, that is, the leading edge slope SL of the echo pulse, and the calculation formula (1) is:

[0078]

[0079] The leading edge slope value of the echo pulse monotonically changes within the measurement range with the change in the intensity of the echo pulse, and there is a monotonic correspondence between this leading edge slope value and the extracted value of the reception time of the echo pulse (as Figure 6As shown, there is also a monotonic correspondence between the leading-edge slope value of the echo pulse and the measurement error of the flight time. By obtaining the leading-edge slope value of the echo pulse, calculating the corresponding measurement error of the flight time, calibrating the flight time, and further obtaining a more accurate ranging result.

[0080] According to a preferred embodiment of the present invention, as Figure 8A 、 Figure 8B shown, the present invention also provides a method 30 for obtaining the intensity peak value PV of an echo pulse, including:

[0081] In step S301, set a first threshold value VL and a second threshold value VH;

[0082] In step S302, according to the first threshold value VL, obtain the first moment T1 corresponding to the leading edge of the echo pulse and the second moment T2 corresponding to the trailing edge of the echo pulse;

[0083] In step S303, according to the second threshold value VH, obtain the third moment T3 corresponding to the leading edge of the echo pulse and the fourth moment T4 corresponding to the trailing edge;

[0084] In step S304, obtain the low-threshold pulse width WL according to the time difference between the first moment T1 and the fourth moment T4, and obtain the high-threshold pulse width WH according to the time difference between the second moment T2 and the third moment T3;

[0085] In step S305, based on the low-threshold pulse width WL and the high-threshold pulse width WH, as well as the first threshold value VL and the second threshold value VH, obtain the intensity peak value PV of the echo pulse. Specifically, as Figure 8B shown, the calculation formula (2) for the intensity peak value PV is:

[0086]

[0087] Wherein the first threshold value VL is a low threshold value, used to reduce noise and filter out ambient light signals, the second threshold value VH is a high threshold value, used to judge the intensity of the echo signal or extract the reception moment of the echo signal. WH is the high-threshold pulse width, and WL is the low-threshold pulse width.

[0088] During actual use, substitute the measured time quantity and the signal intensity corresponding to this time quantity into the above formula, calculate the leading-edge slope value SL and the intensity peak value PV, and then calibrate the flight time using the leading-edge slope value SL and / or the intensity peak value PV.

[0089] According to a preferred embodiment of the present invention, as Figure 9A 、 Figure 9BAs shown, wherein step S302 (step S202): According to the first threshold VL, obtain the first moment T1 corresponding to the leading edge of the echo pulse and the second moment T2 corresponding to the trailing edge of the echo pulse; step S303 (step S203): According to the second threshold VH, obtain the third moment T3 corresponding to the leading edge of the echo pulse and the fourth moment T4 corresponding to the trailing edge. The specific implementation device includes:

[0090] Input the echo pulse signal into the non-inverting terminal of the first comparator, input the first threshold VL into the inverting terminal of the first comparator. When the comparison result between the intensity of the echo pulse and the first threshold VL flips for the first time, obtain the first moment T1 through the time-to-digital converter. When the comparison result between the intensity of the echo pulse and the first threshold VL flips for the second time, obtain the second moment T2 through the time-to-digital converter;

[0091] Input the echo pulse signal into the non-inverting terminal of the second comparator, input the second threshold VH into the inverting terminal of the second comparator. When the comparison result between the intensity of the echo pulse and the second threshold VH flips for the first time, obtain the third moment T3 through the time-to-digital converter. When the comparison result between the intensity of the echo pulse and the second threshold VH flips for the second time, obtain the fourth moment T4 through the time-to-digital converter;

[0092] Wherein Figure 9A In the preferred embodiment, sampling is performed separately by multiple time-to-digital converters. Figure 9B In the preferred embodiment, the echo signal is sampled by a single time-to-digital converter.

[0093] According to a preferred embodiment of the present invention, step S105 in calibration method 10: The step of calibrating the obtained distance information according to the calibration reference quantity includes:

[0094] Calibrate the distance information through a calibration curve according to the calibration reference quantity and the measured distance information.

[0095] According to a preferred embodiment of the present invention, as Figure 10 shown, the present invention also provides a method 40 for obtaining a calibration curve, including:

[0096] In step S401, continuously send emission pulses to the target object, receive the echo pulses reflected by the target object with the optical receiving device, and obtain the distance of the target object through the time of flight;

[0097] In step S402, scan multiple different targets to generate scan information. The scan information can be represented by multiple data points, where the data points are determined according to the calibration reference quantity and the distance information. Preferably, the calibration reference quantity is the leading edge slope or intensity peak of the echo pulse;

[0098] In step S403, a calibration curve for calibration is obtained through linear fitting. The process of curve fitting includes: Given the true time of flight, denoted as Ty, when the lidar is uncalibrated, the measured time of flight is Tx. A function regarding the leading edge slope or intensity peak of the echo pulse is obtained based on the scanning information. The fitting curve is: Ty = Tx - A*, where A* is obtained by curve fitting with the leading edge slope as the abscissa, or Ty = Tx - B*, where B* is obtained by curve fitting with the intensity peak as the abscissa. The obtained A* and B* are the fitting curves regarding the leading edge slope and intensity peak respectively, thereby obtaining the calibration curve.

[0099] Generally, the calibration of the lidar time of flight (and thus the correction of distance information) is for the following situations: One is the deviation caused by the delay in data processing, and this deviation is a fixed value; the other is when the echo signals have different strengths, there will be a drift in the moment of the leading edge of the echo signal, resulting in a deviation in distance information. The latter deviation needs to be obtained by linear fitting of the leading edge slope or intensity peak of echo signals with different strengths. Since the deviation caused by the delay in data processing is a fixed value, it can be brought into the calibration curve as a constant.

[0100] According to a preferred embodiment of the present invention, in order to obtain a more accurate ranging result, the calibration curve is obtained by using the method of piecewise linear fitting.

[0101] The fitting curve is used to correct the time of flight. For example, according to the fitting curve, using the leading edge slope SL or intensity peak PV of the echo pulse obtained in methods 20 and 30, and then calibrating the time of flight according to the calibration curve, and further calculating the accurate distance information.

[0102] According to a preferred embodiment of the present invention, the calibration method 10 provided by the present invention is applicable to a silicon photomultiplier tube or a single photon avalanche diode array as the optical receiving device, wherein the echo pulse is received by the silicon photomultiplier tube and an electrical signal is output.

[0103] According to a preferred embodiment of the present invention, the calibration method 10 further includes:

[0104] According to different ranging ranges, different calibration reference quantities are selected for calibrating the distance information. Preferably, according to the previous measurement results, a calibration reference quantity that is monotonic and has good stability within the ranging range is selected for calibrating the distance information; different calibration reference quantities can be selected for calibration within different ranging ranges.

[0105] Such as Figure 11As shown, the present invention also provides a lidar configured to calibrate the distance information using the calibration method 10 described above. Among them, the transmitting unit emits detection pulses for measuring the distance information between the target object and the lidar. The receiving unit receives the echo of the detection pulse reflected by the target object. The processing unit obtains the flight time based on the time difference between the detection pulse and the echo pulse, obtains the calibration reference quantity based on the echo pulse, and calibrates the flight time according to the calibration curve, thereby calibrating the distance information.

[0106] The present invention also provides a method for calculating the reflectivity of a target object using the intensity peak PV obtained from the echo pulse in method 30. Since the energy of the transmitted pulse is known, the relationship between the intensity peak of the radar echo pulse and the energy of the echo pulse can be established, and then the reflectivity of the target object can be calculated based on the energy of the echo pulse and the energy of the transmitted pulse. According to a preferred embodiment of the present invention, the intensity peak of the echo pulse of the lidar can be calculated by method 30, then the energy of the echo pulse can be calculated based on the intensity peak of the echo pulse, and then the reflectivity of the target object can be calculated based on the energy of the echo pulse and the energy of the transmitted pulse. All of these are within the protection scope of the present invention.

[0107] A preferred embodiment of the present invention provides a calibration method for a lidar and a method for obtaining an appropriate calibration reference quantity. The calibration reference quantity changes monotonically with the intensity of the echo pulse within the measurement range. Using it to calibrate the flight time of the lidar can improve the ranging performance of the lidar, and the calibration accuracy is also significantly improved.

[0108] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A laser radar calibration method, comprising: Sending a detection pulse to the target; Receive the echo pulse after the detection pulse is reflected by the target object through the silicon photomultiplier tube; Acquiring distance information of the target object according to the detection pulse and the echo pulse; Acquiring an intensity peak value of an echo pulse, wherein the intensity peak value of the echo pulse increases monotonically as the intensity of the echo pulse increases; Calibrate the acquired distance information according to the intensity peak value, The step of obtaining the peak intensity of the echo pulse includes: According to the first threshold VL, a first time T1 corresponding to the leading edge of the echo pulse and a second time T2 corresponding to the trailing edge of the echo pulse are obtained; According to the second threshold VH, a third time T3 corresponding to the leading edge of the echo pulse and a fourth time T4 corresponding to the trailing edge are obtained; The low threshold pulse width WL is obtained according to the time difference between the first moment T1 and the fourth moment T4, and the high threshold pulse width WH is obtained according to the time difference between the second moment T2 and the third moment T3; Based on the low threshold pulse width WL and the high threshold pulse width WH, as well as the first threshold VL and the second threshold VH, the peak intensity PV of the echo pulse is acquired.

2. The calibration method as claimed in claim 1, wherein the distance information is obtained by calculating the flight time determined based on the detection pulse and the echo pulse; wherein the flight time is determined based on the pulse leading edge time of the detection pulse and the echo pulse. The calibration method of claim 2 , wherein the intensity peak is used to calibrate the time of flight.

4. The calibration method according to claim 1 , wherein the step of obtaining a first time T1 corresponding to the leading edge of the echo pulse and a second time T2 corresponding to the trailing edge of the echo pulse according to a first threshold value VL, and obtaining a third time T3 corresponding to the leading edge of the echo pulse and a fourth time T4 corresponding to the trailing edge according to a second threshold value VH comprises: Inputting the echo pulse into the non-inverting terminal of the first comparator and inputting the first threshold VL into the inverting terminal of the first comparator, obtaining the first time instant T1 through the time-to-digital converter when the comparison result between the intensity of the echo pulse and the first threshold VL reverses for the first time, and obtaining the second time instant T2 through the time-to-digital converter when the comparison result between the intensity of the echo pulse and the first threshold VL reverses for the second time; The echo pulse is input into the non-inverting terminal of the second comparator, and the second threshold VH is input into the inverting terminal of the second comparator. When the comparison result between the intensity of the echo pulse and the second threshold VH is flipped for the first time, the third moment T3 is obtained through the time-to-digital converter. When the comparison result between the intensity of the echo pulse and the second threshold VH is flipped for the second time, the fourth moment T4 is obtained through the time-to-digital converter.

5. The calibration method according to any one of claims 1 to 3, wherein the step of calibrating the acquired distance information according to the intensity peak comprises: The distance information is calibrated using a calibration curve according to the intensity peak.

6. A lidar configured to calibrate the distance information using the calibration method according to any one of claims 1-5.

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